A majority of the Supreme Court seems inclined to give Americans who are arrested some protection against warrantless searches of their smartphones, but there was no clear agreement among the justices about when and how those added safeguards should apply.

During lively arguments Tuesday about a pair of cases relating to phones seized during arrests, all the members of the court’s liberal wing expressed serious concerns about allowing police the same broad authority to search a smartphone that they have with other items an arrested person may be carrying or have nearby.

Conservative Justice Antonin Scalia, who sometimes rules against the government in Fourth Amendment cases, did not seem deeply troubled by the prospect of a cellphone search during an arrest. However, he suggested that it should be limited to evidence of the crime for which the individual was arrested.

Justice Anthony Kennedy, a Republican appointee who is often the swing vote on the court, mused about the possibility of allowing warrantless cellphone searches in connection with arrests for serious crimes while denying police that right in the case of lesser offenses.

Meanwhile, the most vocal defender of smartphone privacy was Justice Elena Kagan, who said she was troubled by the notion that police could confiscate and copy someone’s phone just because he or she was arrested for driving without a seatbelt.

“Most people carry their lives on smartphones, and that will only grow as young people take over the world,” she declared to laughs from the audience.

Scalia seemed to agree. “It seems absurd that you should be able to search that person’s iPhone” because of an arrest over not wearing a seatbelt, he said.

Some of the justices, who are often faulted for their anachronism, seemed to go out of their way Tuesday to stress how savvy they are about smartphones, other personal electronics and the Internet.

Chief Justice John Roberts suggested that some data found on phones might not be legally protected because the information is essentially public already.

“What about something like Facebook or a Twitter account? …Any privacy interest in a Facebook account is at least diminished because the point is you want these things to be public and seen widely,” Roberts said.

Later in the arguments, he referred to the information gathered by a trendy fitness-tracking device, the Fitbit.

“What about a Fitbit?” Roberts asked. “It’s not his whole life.…Is that something you can look at?”

One aspect of modern life that seemed to confound both Roberts and Scalia, however, was the notion that an ordinary, law-abiding American might have two phones. In questioning one attorney advocating for a warrant requirement, Roberts asked why a suspect might have two phones if not for a drug offense.

Judith Mizner, the federal defender from Boston representing one defendant whose phone was searched, replied she has observed plenty of people with more than one phone. That prompted Roberts to interject, “Really?” and express doubt.

Justice Sonia Sotomayor asked government lawyers who expressed concerns about a suspect wiping his phone remotely why an officer couldn’t just put the phone in “airplane mode,” cutting off its signal. She also asked if the entirety of someone’s iPad would be subject to search if it was sitting near him or her at the time of an arrest.

The arguments in both cases centered around whether cellphones and personal technology have created a fundamentally different world for police, and whether that means that warrants should be required for all searches of electronic devices.

The first case heard Tuesday, Riley v. California, centers on a man who was pulled over for expired tags, after which a search of his car turned up weapons. Both at the scene and at the station after his arrest, police went through David Riley’s phone, finding text messages, contacts, photos and video that implicated him in gang activity and another crime.

Riley’s lawyer, Stanford Law Professor Jeffrey Fisher, said the ubiquitous nature of smartphones made seizing them particularly invasive of privacy.

“This is the indispensable item. You can’t leave the house without it and consider yourself to be responsible and safe,” he said.

Fisher also said police making an arrest should have been required to get a search warrant that said what kind of information on the phone was fair game before opening it up.

However, several justices said they thought it would be difficult for a magistrate issuing a warrant to try to describe what could be seized and what couldn’t.

“What part of a smartphone is not likely to have pertinent evidence?” Roberts asked.

“Those arguments can be made on an app-by-app basis,” Fisher replied, in what may have been the first time that phrase was ever uttered in the high court.

In an apparent appeal to Scalia and other justices who express concerns about the government invading the sanctity of the home, Fisher repeatedly described the kind of personal information kept on a smartphone as the digital equivalent of information people traditionally kept in their homes.

Fisher also warned that state and local law enforcement are building massive databases using their as-yet-unrestricted access to smartphones at the time of arrests. He said that would be better regulated by requiring warrants through which magistrates can set rules about what kind of data can be retained, for how long and for what purpose — limits some federal magistrates are beginning to insist on.

California Solicitor General Edward Dumont referred several times to possession of a cellphone as a choice, suggesting that those arrested are taking a calculated risk by carrying so much information on their person.

“People do make choices and choices do have consequences,” he said. That argument did not appear to sit well with Kagan and other justices who made clear they view smartphones as a modern necessity, not a luxury.

Riley’s ultimate conviction was appealed to the California Court of Appeals, which upheld his conviction and the evidence collected as a constitutional search. The California Supreme Court declined to hear the case.

The second case, United States v. Wurie, came out of Massachusetts. The defendant, Brima Wurie, was arrested after an apparent drug deal. While in custody, police used his phone’s call logs to find the number for “my house,” which led them to Wurie’s home and more evidence used to support his conviction. The 1st U.S. Circuit Court of Appeals overturned the conviction, saying the cellphone evidence violated Wurie’s Fourth Amendment rights on search and seizure. The appeals court held that a warrant is required to access any data on a suspect’s cellphone upon arrest.

With arguments taking place immediately following the close of Riley, the justices took the opportunity to dive deeper into some of the issues presented in the first case and draw distinctions between the circumstances in the first case, which involved pictures and phone media, and the second, which involved call logs on a flip phone.

Deputy Solicitor General Michael Dreeben, who argued in both, engaged in a lengthy back and forth with Justice Stephen Breyer, traditionally a member of the court’s liberal wing, over the extent of cellphone encryption.

Dreeben argued that the risk of phones self-encrypting while in police custody put evidence at peril, while Breyer expressed skepticism that a criminal would be smart enough to set up encryption in advance but not smart enough to have that triggered 30 seconds after an arrest as opposed to en route to a police station or awaiting a warrant.

Breyer again drew laughter and delight from the audience with his discussion of encryption, asking when what he described as a “bzzzzt” would actually render the data on the phone impossible to achieve.

“Maybe there is such thing,” he mused. Dreeben started to respond he didn’t know what type of phone Breyer had, to which Breyer interjected, “I don’t know either, because I can never get into it.”

During Mizner’s turn, the justices focused on the fact that the “my house” number was arguably in plain view, with Justice Samuel Alito pressing Mizner on what reasonable expectation of privacy an American in 2014 has when they bring their phone with them outside of their homes.

In both cases, the justices seemed to grapple with the notion that existing case law deals with a “pre-digital era,” as Alito put it, and they split on whether cellphones should be considered along the same lines as anything that could have been carried in a briefcase or “billfold,” or whether the extent of data stored on a phone was fundamentally different enough to require new rules.

When Roberts suggested GPS location data was something completely unique to smartphones, Breyer mentioned his wife could have written a note in his pocket with instructions like “turn right.”

“GPS would say if he did in fact turn right,” Roberts noted, to laughter.

Privacy advocates have argued that because of the scope of information a person can carry on their smartphone, warrants should be required to examine their contents. While the cases at hand deal with cellphones, similar questions have been raised about searches of laptops at borders, and experts have questioned whether searches could extend to data stored on the cloud via apps on devices.

The Obama administration contends there is no fundamental difference between cellphones and anything else a person may carry that could be searched upon arrest. In a government brief filed in Wurie, Solictor General Donald Verrilli compared cellphones to the contents of a briefcase, for example, saying officers were able to read and look through any documents or photos people tended to carry on them in hard copy.

Dreeben maintained that position Tuesday, but said that if the court was inclined to provide some protection for smartphones, the federal government would urge the court to adopt Scalia’s suggestion that the search must be related to the crime for which a person was arrested.

The call logs of a suspect would always be reasonable to search without a warrant, though, the government argued in its brief. Alito seemed to back that position.

While a majority of the justices seemed to leaning toward some limits on the extent to which police can search cellphones, there was clear disagreement on what the appropriate standard should be. Roberts seemed skeptical that keeping searches to the evidence related to the crime of arrest would work, given that a reasonable argument could be made to search everything on the phone.